Neurosurgical resection of brain lesions aims to maximize excision while minimizing the risk of permanent injury to the surrounding intact brain tissue and resulting neurological deficits. While direct electrical cortical stimulation at the time of surgery allows the precise identification of essential cortex, it cannot provide information preoperatively for surgical planning. Brain imaging techniques such as functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG) and transcranial magnetic stimulation (TMS) are increasingly being used to localize functionally critical cortical areas before brain surgery. The use of multimodal preoperative information improves the accuracy of preoperative planning and facilitates decision-making regarding the extent and exact location of surgical resections. This manuscript reviews how fMRI and TMS can be used in presurgical settings to map motor as well as higher cognitive functions (i.e. language). Pre-operative fMRI can be used to identify the brain regions that are activated during specific sensorimotor or language tasks. TMS is able to disrupt neuronal processing in the targeted brain area which in turn may affect task performance, if the stimulated cortex makes a critical contribution to the brain functions subserving the task. While the relationship between task and functional activation as revealed by fMRI is correlative in nature, the neurodisruptive effect of TMS reflects a causal effect on brain activity. The use of preoperative fMRI is well established although the number of studies on presurgical language fMRI is still limited. In contrast, the reliability and accuracy of preoperative TMS remains to be determined.
Keywords: Functional magnetic resonance imaging, transcranial magnetic stimulation, preoperative, motor system, language, wada test, fMRI, magnetoencephalography, MEG, TMS, positron emission tomography, PET, single-photon emission computed tomography, SPECT, intraoperative cortical stimulation, ICS, neuroanatomy, temporal gyrus, arcuate fascicle, supramarginal gyrus, SMG, angular gyrus, AG, TMS evoked motor potential, MEP, equivalent current dipole, ECD, somatosensory evoked fields, SEFs